q9400 is socket 775.
For around 200$ you could get i7-860 if you find one, that will be faster in multi core by around 40-60%, but is almost the same at single core.
Depending on games you play it may or may not make a difference.
You see socket 1156 is getting old and prices go way too high due to old technology and low demand.
You could find i7-860 second hand for around 110$ i guess, but as i said i am not sure how much difference you will see with it.
If you go for skylake you will definitely see a boost in performance both in single and multi core, where as i said for 200$ you will get better CPU + MB + RAM and will be ready to upgrade CPU when you have enough budget.
Have in mind that incoming Kaby-lake will be the same socket, which means you could even upgrade later on to it.